SYSTEMS AND METHODS FOR PRINTING METAL LINES AND PATTERNS AT HIGH RESOLUTION

Abstract

A solvent layer is coated on a metal layer carried by a donor substrate, allowing the fabrication of solid metal lines at a high resolution. The laser jetting involves ejecting metal particles, constrained within a solvent membrane, from the metal layer. Once the metal particles have been deposited onto a receiver substrate, the solvent can be evaporated. Since this printing procedure can be performed with the solvent layer in direct contact with the receiver substrate or separated therefrom by a small distance, the resolution of the metal lines can be very high and depends directly on the laser spot size and defocus. The solvent constrains the droplet size of the metal particles, which can increase or maintain the resolution of the laser beam. As this process is a continuous sequence production, the metal line production can be performed at a very rapid rate.

Claims

1. A printing system, comprising: a donor substrate; a coating unit configured to coat a surface of the donor substrate with a metal layer and to coat a surface of the metal layer with a solvent layer; and a printing unit configured to direct a laser beam towards the donor substrate so as to jet metal particles from the metal layer towards a receiver substrate, wherein the metal particles are constrained within a solvent membrane formed by the solvent layer while being jetted towards the receiver substrate.

2. The printing system of claim 1, wherein the solvent layer has a uniform thickness.

3. The printing system of claim 1, further comprising a high frequency laser to generate the laser beam.

4. The printing system of claim 1, wherein the laser beam comprises radiation at one or more wavelengths, and wherein the donor substrate is transparent to the radiation at the one or more wavelengths.

5. The printing system of claim 1, wherein a thickness of the metal layer is between one nanometer and one micron.

6. The printing system of claim 1, wherein the coating unit is configured to form the metal layer on the donor substrate by a thermal coating process.

7. The printing system of claim 1, wherein the solvent layer comprises a non-polar solvent with a boiling point between 50-150° C.

8. The printing system of claim 1, wherein the donor substrate comprises a continuous transparent film substrate.

9. A printing system, comprising: a donor substrate; a coating unit configured to coat a surface of the donor substrate with a dielectric layer, to coat a surface of the dielectric layer with a metal layer and to coat a surface of the metal layer with a solvent layer; and a printing unit configured to direct a laser beam towards the donor substrate so as to jet metal particles from the metal layer towards a receiver substrate, wherein the metal particles are constrained within a solvent membrane formed by the solvent layer while being jetted towards the receiver substrate.

10. A method, comprising: coating a surface of a donor substrate with a metal layer; coating a surface of the metal layer with a solvent layer; and directing a laser beam towards the donor substrate so as to jet metal particles towards a receiver substrate, wherein the metal particles are constrained within a solvent membrane formed by the solvent layer while being jetted towards the receiver substrate.

11. The method of claim 10, wherein the solvent layer has a uniform thickness.

12. The method of claim 10, wherein the solvent layer comprises a non-polar solvent with a boiling point between 50° C.−150° C.

13. The method of claim 10, further comprising evaporating solvent from the metal particles in a controlled environment or in ambient conditions.

14. The method of claim 10, further comprising forming conductive metal lines and patterns on a surface of the receiver substrate from the metal particles.

15. The method of claim 10, wherein the solvent layer contacts the receiver substrate during the jetting of the metal particles.

16. The method of claim 10, wherein the solvent layer is separated from a surface of the receiver substrate by 500 microns or less during the jetting of the metal particles.

17. A method, comprising: coating a surface of a donor substrate with a dielectric layer; coating a surface of the dielectric layer with a metal layer; coating a surface of the metal layer with a solvent layer; and directing a laser beam towards the donor substrate so as to jet metal particles towards a receiver substrate, wherein the metal particles are constrained within a solvent membrane formed by the solvent layer while being jetted towards the receiver substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which:

[0025] FIG. 1A depicts a cross sectional view showing the printing of metal from a donor substrate, in which metal particles are sprayed from the donor substrate onto a receiver substrate.

[0026] FIG. 1B depicts a cross sectional view showing the printing of metal from a donor substrate, in which a solvent envelope filled with metal particles is ejected from the donor substrate towards the receiver substrate, in accordance with one embodiment of the invention.

[0027] FIG. 2A depicts a cross sectional view showing a donor substrate that has been coated with a metal layer, in accordance with one embodiment of the invention.

[0028] FIG. 2B depicts the donor substrate of FIG. 2A that has been additionally coated with a solvent layer, in accordance with one embodiment of the invention.

[0029] FIG. 2C depicts a cross sectional view showing a region of the metal layer being heated by a laser beam, in accordance with one embodiment of the invention.

[0030] FIG. 2D depicts the effect of the laser heating, in which a portion of the metal layer is transformed into metal particles, in accordance with one embodiment of the invention.

[0031] FIG. 2E depicts a cross sectional view showing metal particles being constrained within a solvent membrane, in accordance with one embodiment of the invention.

[0032] FIG. 2F depicts a cross sectional view showing the metal particles landing on the receiver substrate, in accordance with one embodiment of the invention.

[0033] FIG. 2G depicts a cross sectional view showing the evaporation of the solvent as well as the sintering of the metal particles, in accordance with one embodiment of the invention.

[0034] FIG. 2H depicts a cross sectional view of a metal structure on the receiver substrate after the metal particles have been sintered, in accordance with one embodiment of the invention.

[0035] FIG. 3 depicts a cross sectional view showing an alternative coating of the donor substrate in which a dielectric layer is sandwiched between the donor substrate and the metal layer, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention provides a much faster way to fabricate metal lines and patterns on a receiver substrate at a high resolution by applying a solvent layer to metal-coated donor substrate. The laser jetting involves ejecting metal particles, constrained within a solvent membrane, from a metal layer coated on the donor substrate. Once the metal particles have been deposited onto a receiver substrate, the solvent can be evaporated.

[0037] Since this printing procedure can be performed with the solvent layer in direct contact with the receiver substrate (or separated therefrom by a small distance), the resolution of the metal lines is very high and depends directly on the laser spot size and defocus. The solvent constrains the droplet size of the metal particles, which can increase or maintain the resolution of the laser beam. As this process is a continuous sequence production, the metal line production can be performed at a very rapid rate.

[0038] Before describing the invention in detail, it is helpful to present an overview. The invention generally relates to the laser-assisted deposition of metal particles from a donor substrate 12 onto a receiver substrate 18. As illustrated in the printing system 100 depicted in FIG. 1A, a printing unit 10 is used to direct a laser beam 20 towards a donor substrate 12 that has been coated with a metal layer 14, causing metal particles 22 to be jetted towards the surface of a receiver substrate 18. The jetted metal particles 22, however, travel in uncontrolled stream (e.g., in a spray or mist form) that can diffuse in air to distant locations. Such uncontrolled (or loosely controlled) trajectory of the metal particles 22 is undesirable as it reduces the resolution at which the printing of metal on the receiver substrate 18 can be performed as well as can cause contamination of equipment in the surrounding workspace.

[0039] To address such shortcoming of the printing system 100, a surface of the metal layer 14 (facing the receiver substrate 18) may be coated with a solvent layer 16, as depicted in the printing system 102 of FIG. 1B. When the printing unit 10 directs the laser beam 20 towards the donor substrate 12 in the printing system 102, the metal particles 22 are constrained within a solvent membrane 24 as the metal particles 22 are released from the metal layer 14. Such solvent membrane 24 filled with metal particles 22 then is then jetted towards the receiver substrate 18. The resulting effect is that the trajectory of the metal particles 22 can be much more stringently controlled (e.g., trajectory can be controlled to be perpendicular to the surface of the receiver substrate 18). Accordingly, the resolution at which the metal particles 22 can be printed on the receiver substrate 18 can be greater than the resolution possible from the printing system 100 depicted in FIG. 1A.

[0040] In one embodiment, the donor substrate 12 may be a film of plastic or glass. In one embodiment, the donor substrate 12 is a continuous transparent film substrate. In a preferred embodiment, the donor substrate 12 is a transparent plastic film to allow a direct contact to more easily be formed between the solvent layer 16 and the receiver substrate 18. One benefit of a direct contact is an increase in the final printing resolution. However, the same printing technique can still be applied with the donor substrate 12 separated by some distance from the receiver substrate 18, albeit with a possible reduction in the printing resolution.

[0041] In one embodiment, the donor substrate 12 may be transparent to the wavelengths of radiation present in the laser beam 20. The radiation may include infra-red (IR) light, visible light or ultra-violet (UV) light. Therefore, the films that can be used for the process are almost unlimited, because almost any film of material used as the donor substrate 12 will be transparent to at least one of the wavelengths mentioned above.

[0042] The metal layer 14 coating a surface of the donor substrate 12 can be created by any known chemical or physical coating mechanism. However, in a preferred embodiment, a thermal coating process which deposits metal from a metal target is used, because such a process is capable of depositing a very precise and uniform metal layer 14 on the donor substrate 12. The metal layer 14 can include any metal, but in the most important application of creating metal conduction lines on printed circuit boards (PCBs) and other surfaces, the metal layer 14 includes copper.

[0043] The key properties of the solvents to consider when selecting the solvent are its compatibility to the metal in the metal layer 14 and its boiling point. The reason is that a non-compatible solvent can increase the oxidation of the metal during the laser jetting or can increase the occurrence of other side reactions. Therefore, it is important to choose a solvent with a low tendency to react with the metal in use. It is also important to choose a solvent with a high enough boiling point so that it will not evaporate from the donor substrate 12 prior to the jetting of the metal particles 22 at the start of the process. It is also important that the solvent will have a low enough boiling point so that it will evaporate from the metal particles 22 during or right after the jetting.

[0044] Some metals (e.g., metals that do not tend to react) can be jetted with the aid of any solvent with a high enough boiling point (e.g., water). Other metals will need to be jetted with non-polar solvents such as ISOPAR™ with a medium boiling point or polar solvents such as tetrahydrofuran (THF). However, in a preferred embodiment, solvents with respective boiling points between 50-150° C. and a low number of reactive components (i.e., inert solvents) are used.

[0045] FIGS. 2A-2H depict a sequence of drawings to illustrate a coating process using a coating unit 11, followed by a metal jetting process using a printing unit 10. As depicted in FIG. 2A, a donor substrate 12, more specifically its bottom surface, is first coated with a metal layer 14. As previously explained, the type of material used for donor substrate 12 is almost unlimited. Almost any plastic can be used, and even colored films can be considered if they are transparent to the wavelength(s) of the laser beam 20. Furthermore, the thickness of the metal layer 14 on the donor substrate 12 can be as thin as one nanometer or as thick as one micron. Therefore, the variety of metals and metal thicknesses that can be printed by the jetting process is very high.

[0046] However, the most important application for the current process is depicted in FIG. 2A, in which a transparent donor substrate 12 is coated with a copper layer 14. In a preferred embodiment, the donor substrate 12 may be a polyester (PET) film with a thickness of microns that is coated by a copper layer with a thickness of 100 microns.

[0047] As depicted in FIG. 2B, the surface of the metal layer 14 facing the receiver substrate 18 may be coated with a layer of solvent 16. In a preferred embodiment, the solvent is ISOPAR™ with a 63° C. boiling point and no reactive components on its backbone.

[0048] As depicted in FIG. 2C, a printing unit 10 may direct a laser beam 20 towards the donor substrate 12, which causes a region 26 of the metal layer 14 to be heated. As previously mentioned, the laser beam 20 may include light in the ultra-violet (UV), infra-red (IR) and/or visible spectrums. The energy emitted by the laser (not depicted) and the distance between the laser (not depicted) and the focal point of the laser beam 20 on the metal layer 14 will determine the spot size and the effect of the laser beam 20 on the metal layer 14. In one embodiment, the laser is a high-frequency laser.

[0049] FIG. 2C illustrates the effect of shining the laser beam 20 on the metal-coated donor substrate 12. Heat is absorbed on the side of the metal layer 14 facing the printing unit 10 and metal particles 22 (e.g., on the scale of nanometers) begin to form, as depicted in FIG. 2D. At this point in the process, the presence of the solvent layer 16 becomes relevant: instead of an uncontrolled stream of metal particles 22 that can travel in the air to all directions, the solvent layer 16 constrains the trajectories of the respective metal particles 22. As a result of the solvent layer 16, the metal particles 22 are enveloped within a solvent membrane 24 as the metal particles 22 travel toward the surface of the receiver substrate 18 in a direction normal to the surface of the donor substrate 20, as depicted in FIG. 2E.

[0050] When the solvent membrane 24 with the metal particles 22 therein contacts the surface of the receiver substrate 18, as depicted in FIG. 2F, the solvent starts to evaporate. The evaporation can occur at ambient conditions if a slow evaporation is desired. Otherwise, the evaporation can occur more quickly at higher temperatures by heating the surface of the receiver substrate 18 with a heater, a stream of hot air, or the laser beam 20 to sinter the metallic particles, as depicted in FIG. 2G. In one embodiment, the evaporation of the solvent may take place in a controlled environment or in ambient conditions.

[0051] At the end of the printing process, the sintering of the metal particles 22 forms a metallic conductive pattern 28 on the surface of the receiver substrate 18. The conductivity of the metallic conductive pattern 28 can equal the conductance of a pure metal since no organic material is present in the final metallic conductive pattern 28, as shown in FIG. 2H.

[0052] FIG. 3 depicts an alternative embodiment in which a dielectric layer 13 is disposed between the donor substrate 12 and the metal layer 14. The dielectric layer 13 may include an adhesive such as glue to enhance the adhesion of the metal layer 14 to the donor substrate 12, which is advantageous for some types of metals which would otherwise have difficulty adhering to the donor substrate 12.

[0053] Thus, systems and methods for printing metal lines and patterns at high resolution have been described. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

LIST OF REFERENCE NUMERALS

[0054] 10 Printing unit [0055] 11 Coating unit [0056] 12 Donor substrate [0057] 13 Dielectric layer [0058] 14 Metal layer [0059] 16 Solvent layer [0060] 18 Receiver substrate [0061] 20 Laser beam [0062] 22 Metal particles [0063] 24 Solvent membrane [0064] 26 Heated region of metal layer [0065] 28 Deposited metal [0066] 100 Printing system [0067] 102 Printing system